Where did the water come from? Some of it may have come from the comets. Some may have come from asteroids. Icy planetesimals may have deposited their water when they crashed into the young Earth. It is possible that hydrogen from inside the Earth contributed. The collision that formed the Moon gave Earth its water, according to one hypothesis.
There is evidence to support all of the hypotheses.
New research shows that the Sun and its Solar Wind may have helped deliver some water.
The oceans hold about 1.37 1021 kg of water. That is one sextillion seventy quintillion kilograms. The amount of lakes, rivers, ice, and water vapour is five hundred quintillion kilograms. About 70% of the Earth is covered by water. Earth is unique among planets because it has sub-surface oceans on a few moons. Without all that water, we wouldn't be here and there wouldn't be life. The source of that water is a mystery.
The material around the Sun became a star after Earth formed. It is the same material as the other planets and moons. Earth formed close to the Sun, so it didn't have the same amount of water as the planet did. Iron, oxygen, Silicon, sulphur, and magnesium make up the majority of Earth's mass. Water has a much lower condensation temperature than those materials so it would have been vapour.
Water would have been deposited into icy asteroids, planetesimals, and comets further from the Sun. The idea of an extraplanetary source for Earth's water is still alive. Evidence shows that Jupiter sent icy asteroids from the outer Solar System to the inner Solar System after the planets formed. Enough water arrived by asteroids and comets to account for Earth's water after a long period of time.
This artist's view shows a possible primordial asteroid, 2004 EW95. The rocky components were altered by the presence of water. The idea that asteroids delivered water to Earth is reinforced by this evidence. M. Kornmesser is a scientist at the European Southern Observatory.
There is a problem with the asteroid water-delivery theory. The idea is centred on asteroids with hydrated minerals. There is a difference in the composition of water on asteroids and Earth. There is a missing source of water that is different from the C-type asteroids.
The Sun and its solar wind can help explain Earth's water, according to a new paper.
The paper is titled Solar wind contributions to Earth's oceans. The journal Nature Astronomy has published it and the first author is a University of Glasgow PhD student.
Professor Phil Bland is from the Space Science and Technology Center. The hypothesis that icy asteroids delivered Earth's water was explained in a press release by Dr. Bland. Water was carried to Earth in the final stages of its formation on C-type asteroids, however, previous testing of the isotopic 'fingerprint' of these asteroids found they, on average, didn't match with the water found on Earth.
Bland said that the solar wind created water on the surface of tiny dust grains and that the lighter water likely provided the rest of the Earth's water.
The results are based on samples from an asteroid. The Hayabusa mission returned samples from Itokawa. Itokawa had abundant water. That discovery made the idea of Earth getting its water from asteroids stronger. Itokawa is an S-type asteroid, which means it formed much further from the Sun than Earth did, out in the cold reaches of the Solar System where water would freeze rather than evaporate.
Hayabusa visited the asteroid Itokawa in 2005. Credit: JAXA
The researchers looked at the tiny samples from Itokawa. They found that the H+ in the solar wind creates water and silicate minerals on the surface of the asteroid.
Professor Bland said that the new solar wind theory was based on the analysis of tiny fragments of an S-type near-Earth asteroid called Itokawa, which was collected by the Japanese space probe Hayabusa and returned to Earth in 2010.
We were able to take an incredibly detailed look inside the first 50 micrometres of the surface of Itokawa dust grains, which we found contained enough water that, if scaled up, would amount to about 20 litres.
There are surface patterns on the dust particles from Itokawa. The image is from JAXA.
In their paper, the authors write that they used atom probe tomography to observe an average 1?mol% enrichment in water and hydroxyls in the solar-wind-irradiated rim of an olivine grain from the S-type asteroid Itokawa. We have proof that H+ irradiation of silicate mineral surfaces produces water.
The team believes that the mechanism is widespread in the Solar System. The results suggest that the Itokawa regolith could contain 20?l?m?3 of solar-wind-derived water and that it is probably ubiquitous on airless worlds throughout the universe.
The discovery helps explain how Earth got all its water. If the researchers are correct, we have a more complete picture of the early Earth. The early Solar System may have provided a means to recreate Earth's current water isotope ratios if the production of this isotopically light water reservoir by solar wind implantation into fine-grained silicates had been a particularly important process.
An artist has a picture of the sun. asteroids have no protection from Earth's magnetosphere. H+ can hit the surface of asteroids and produce water. The image was taken by the ESO/K.
The discovery may mean something to future astronauts.
The presence or lack of water will allow and restrict our space-faring activities. If the process of creating water by the solar wind is widespread, it means that asteroid and lunar regolith have water for the taking.
One of the barriers to future space exploration is how astronauts would get enough water.
The same space weathering process that created water on Itokawa may be the same one that created water on other airless planets, meaning astronauts may be able to process fresh supplies of water straight from the dust on a planet's surface, such as the Moon.
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